1. Field of the Invention
The present invention relates to a novel thermosetting powder coating material which forms coatings having improved slipping property and water repellency by compounding a synthetic wax or natural wax with a fluororesin powder coating material having a reactive group for crosslinking in the molecule, which coatings have excellent adhesion property to substrates, particularly to stainless steel, and excellent impact resistance imparted thereto by a compound having a coupling group compounded in it.
2. Description of the Prior Art
Application of thermoplastic flouroresin powders comprising tetrafluoroethylene resins to various areas has been proposed and practical applications, have been made to adhesion-free applications such as coating of frying pans and rice cookers, by taking advantage of the low surface tension of flouroresins (Laid Open Japanese Patent Applications Showa 61-181567, Showa 61-151571 and Showa 61-181572).
However, the applications described above have problems, e.g., melt coating of the resin requires a high temperature of around 400.degree. C. and adhesion to substrates is not satisfactory.
A thermosetting flouroresin powder coating material was developed for solving these problems (Laid Open Japanese Patent Application Heisei 1-103670).
This thermosetting flouroresin powder coating material can form a coating layer by baking at a temperature of 200.degree. C. or lower and the coating has good weatherability and acid resistance as well as good adhesion to substrates other than stainless steel in comparison with tetrafluoroethylene resins which had been known before. This material has been widely used for these reasons. However, this material has drawbacks, viz., water repellency and slipping property of a coating layer, which are advantages of flouroresins in general, are inferior to a great extent because it contains less fluorine than conventional flouroresin powders containing tetrafluoroethylene resins and it does not have sufficient adhesion to stainless steel.
Because of these drawbacks, treatment of coating with colored chemicals, such as chromate treatment, or coating with a primer having good adhesion to substrates, such as an epoxy resin coating material, was necessary when the material described above is used to coat a substrate like stainless steel. When a chromium oxide treating agent is used for the clear coating with the flouroresin power coating material, problems of coloring caused by the treating agent and treatment of waste water containing chromium oxide compounds arise. When the primer coating is applied, another problem arises, viz., separation tends to occur between the primer coating layer and the finished flouroresin coating layer because weatherability of the primer coating layer is inferior to the flouroresin coating layer. For this reason, a flouroresin powder coating exhibiting a high grade of clearness which takes full advantage of the quality of a substrate material is not easily attained. Furthermore, even in colored coating using the flouroresin powder coating materials, the chromium oxide coating treatment or the primer coating treatment is necessary and the process of the coating tends to be complicated.